Alkylene glycols, such as monoalkylene gycols, are of continued commercial interest and the demand for the same has increased. For example, monoalkylene glycols are used in anti-freeze compositions, as solvents and as base materials in the production of polyalkylene terephthalates, e.g., for fibers and bottles.
Alkylene glycols are typically prepared from their corresponding alkylene oxide utilizing a liquid phase hydrolysis process. In commercial production, the hydrolysis reaction is performed without a catalyst by adding a large excess of water, e.g., 15 to 30 moles of water per mole of alkylene oxide. The prior art hydrolysis reaction is a nucleophilic substitution reaction, in which ring opening of the alkylene oxide occurs and water serves as the nucleophile.
Because initially formed monoalkylene glycol also acts as a nucleopile, a mixture of monoalkylene glycol, dialkylene glycol and higher alkylene glycols is typically formed. In order to increase the selectivity to monoalkylene glycol, it is necessary to suppress the secondary reaction between the primary product and the alkylene oxide, which competes with the hydrolysis of the alkylene oxide.
One effective technique for suppressing the secondary reaction is to increase the amount of water present in the reaction mixture. Although this prior art technique improves the selectivity towards the production of the monoalkylene glycol, it creates a problem in that large amounts of water have to be removed. Removing such additional water increases production costs because such a removal process is energy intensive and requires large-scale evaporation/distillation facilities.
A number of prior art publications show that higher selectivity to monoalkylene glycols can be achieved if the reactions are conducted using heterogeneous catalytic processes, such as, for example, with catalysts based on an ion exchange resin as disclosed in EP-A-156,449 (metalate-containing anion exchange resins); JP-A-57-139026 (anion-exchange resin in the halogen form); Russian Patent Nos. 2002726 and 2001901 (anion exchange resin in the bicarbonate form); WO/20559A (anion exchange resin); and WO 97/33850 (anion exchange resin).
The literature also describes various reactor arrangements that can be used in such catalytic processes. For example, U.S. Pat. No. 6,160,187 describes several arrangements of an adiabatic reactor in combination with heat exchangers. In accordance with the '187 patent, a downflow operation is preferred over an upflow operation since downflow operations reportedly have specific advantages over an upflow process.
Despite all of the advances made in the catalytic hydrolysis of alkylene oxides, there is a continued need for providing a new and improved process of producing monoalkylene glycol from the corresponding alkylene oxides.